i replaced a regular switch with a caseta and now the light just turns on full blast, won’t dim at all.

Diagnosis

The primary cause of a Lutron Caseta dimmer failing to dim and remaining at full brightness is a "reversed polarity" installation. In a standard mechanical toggle switch, the order of the wires doesn't matter because it is a simple break in the circuit. However, the Caseta dimmer is an electronic device that requires a specific flow of current to manage the voltage modulation (TRIAC dimming) sent to the bulb. If the Line (power from the panel) and Load (wire to the light) are swapped, the internal circuitry cannot properly regulate the voltage, causing the switch to default to a "fail-safe" full-on state. Another common cause is a bulb incompatibility. Caseta dimmers are designed for specific load types. If you are using non-dimmable LED bulbs or low-quality LEDs that do not meet the minimum wattage threshold for the dimmer, the switch cannot establish a stable dimming curve. This results in the light either staying at 100% brightness or flickering violently when you attempt to lower the level. You can confirm a wiring error if the switch responds to the button presses (the LED indicator lights up) but the actual light fixture ignores the dimming commands.

How to Fix It

To resolve the polarity issue and restore dimming functionality, follow these precise steps:

1. Shut off the power at the circuit breaker panel. Do not rely on the switch itself to cut power.
2. Remove the wall plate and unscrew the dimmer from the electrical box. Pull the unit forward to expose the wiring.
3. Identify the wires. The "Line" wire is the hot feed coming from your breaker panel. The "Load" wire is the one leading directly to the light fixture. Use a non-contact voltage tester to identify the Line wire by briefly turning the breaker back on; the wire that remains hot while the switch is disconnected is your Line. Turn the breaker back off before proceeding.
4. Disconnect the wires from the wire nuts. Ensure the black wire from the Lutron dimmer (Line) is connected specifically to the hot feed from the panel.
5. Connect the black wire with the white stripe (Load) from the Lutron dimmer to the wire leading to the light fixture.
6. Ensure the green ground wire is securely fastened to the copper or green ground wire in the box.
7. Tuck the wires neatly into the box, ensuring no wires are pinched behind the dimmer body, and screw the unit back into the wall.
8. Restore power and test the dimming range.

If That Didn't Work

• Check Bulb Compatibility: Replace your current bulbs with Lutron-certified dimmable LEDs. If you are using "non-dimmable" LEDs, they will either stay at full brightness or flicker. Look for the "Dimmable" label on the bulb base. If you have a mix of different brands of LEDs in one fixture, this can cause a load imbalance; replace all bulbs with the same brand and model.
• Adjust the Low-End Trim: The dimmer may be set to a high minimum brightness. To adjust the trim: Press and hold the top and bottom buttons simultaneously for about 5 seconds until the LED indicator flashes. Use the buttons to adjust the lowest dimming level to your preference, then press the top and bottom buttons again to save.
• Verify Load Type: If you are controlling an electronic transformer or a specific type of low-voltage halogen, you may have the wrong model. The Caseta PD-6WCL is for most LEDs and Incandescents, but certain specialty loads require a different dimmer model to prevent "full-blast" behavior.
• Test for Neutral Leakage: If you have a neutral wire in the box that is touching the load wire or if there is a short in the junction box, the dimmer may bypass the control circuit. Ensure all wire nuts are tight and no bare copper is touching other terminals.

Heads Up

• Avoid Overloading: Ensure you are not exceeding the maximum wattage for your specific model (typically 600W for incandescents or 150W for LEDs). Overloading can cause the dimmer to overheat and default to full power.
• Avoid "Daisy Chaining" Dimmer-Compatible Bulbs: Some cheap LED bulbs have built-in dimmers. Using these with a Caseta switch creates a "dimmer-on-dimmer" conflict, which often results in the light staying at 100% or buzzing.
• Wire Tightness: Always use the provided wire nuts and ensure the connection is "tug-tested." Loose connections in smart switches can cause intermittent power surges that may damage the internal capacitors.